There is some reason to use tails over whonix if is not for unknow computer or for not leave any data in the system?
All depends on the use case, check this comparison between the two in detail.
Whonix could be considered as an “install once, spend time setting up, use permanently” type of operating system, It’s host-dependent. It also has many security features that Tails don’t have.
while Tails functions more like a disposable or portable system that leaves no trace behind after usage. (hence amnestic)
I could list pros and cons about both operating systems, but both are obviously great in what they do. It just depends on what YOU want to do with it and your personal OPSEC.
The main appeal behind Tails is that it is built to be a live operating system which leaves no data on the device used after it is shut down. If you do not want or need the “amnesia” Tails offers, Whonix in a VM is probably your best bet. Just be mindful that the anonymity and privacy offered by Whonix is somewhat dependant on your host operating system. If you’re using Whonix on top of Windows (for example), you probably shouldn’t expect perfect privacy.